Bottom Line:
The accurate measurement of arterial wave properties in terms of arterial wave transit time (τw) and wave reflection factor (Rf) requires simultaneous records of aortic pressure and flow signals.However, in clinical practice, it will be helpful to describe the pulsatile ventricular afterload using less-invasive parameters if possible.Arterial wave reflections were derived using the impulse response function of the filtered aortic input impedance spectra.

Affiliation: Department of Physiology, College of Medicine, National Taiwan University, Taipei, 100, Taiwan.

ABSTRACTThe accurate measurement of arterial wave properties in terms of arterial wave transit time (τw) and wave reflection factor (Rf) requires simultaneous records of aortic pressure and flow signals. However, in clinical practice, it will be helpful to describe the pulsatile ventricular afterload using less-invasive parameters if possible. We investigated the possibility of systolic aortic pressure-time area (PTAs), calculated from the measured aortic pressure alone, acting as systolic workload imposed on the rat diabetic heart. Arterial wave reflections were derived using the impulse response function of the filtered aortic input impedance spectra. The cardiovascular condition in the rats with either type 1 or type 2 diabetes was characterized by (1) an elevation in PTAs; and (2) an increase in Rf and decrease in τw. We found that an inverse linear correlation between PTAs and arterial τw reached significance (τw = 38.5462 - 0.0022 × PTAs; r = 0.7708, P

f2: Modulus (A) and phase (B) of the Zi in the same rat shown in Fig. 1, and a Dolph-Chebychev weighting function with order 24 (C) and the impulse response functin curve (D) derived from the filtered Zi shown in A and B. In (C), this Dolph-Chebyshev filter is used to reduce the effects of truncation of the impedance. In (D), the long arrow shows the discrete reflection peak from the body circulation and the short arrow indicates the initial peak as a reference. Half of the time difference between the appearance of the reflected peak and the initial peak approximates the arterial τw in the lower body circulation. In this case, the arterial τw was 27.9 ms. Zi, aortic input impedance spectra; τw, wave transit time.

Mentions:
Although the impulse response of the arterial system is the time domain equivalent of its input impedance in the frequency domain, they emphasize different aspects of the system. Figure 2 shows the aortic input impedance (Zi) and its corresponding impulse response of the same normal rat shown in Fig. 1. The impedance modulus fell steeply from a high value at zero frequency (i.e., peripheral resistance) to extremely low values at high frequencies that fluctuated around the aortic characteristic impedance (Zc) (Fig. 2A). The impedance phase indicates the delay between the corresponding pressure and flow components (Fig. 2B). By contrast, Fig. 2D shows the 2 discrete reflection peaks in the impulse response curve, which was calculated through the inverse transformation of Zi filtered by a Dolph-Chebychev weighting function (Fig. 2C). Half of the time difference between the long and short arrows approximates the arterial τw in the lower body circulation. In this case, the arterial τw was 27.9 ms.

f2: Modulus (A) and phase (B) of the Zi in the same rat shown in Fig. 1, and a Dolph-Chebychev weighting function with order 24 (C) and the impulse response functin curve (D) derived from the filtered Zi shown in A and B. In (C), this Dolph-Chebyshev filter is used to reduce the effects of truncation of the impedance. In (D), the long arrow shows the discrete reflection peak from the body circulation and the short arrow indicates the initial peak as a reference. Half of the time difference between the appearance of the reflected peak and the initial peak approximates the arterial τw in the lower body circulation. In this case, the arterial τw was 27.9 ms. Zi, aortic input impedance spectra; τw, wave transit time.

Mentions:
Although the impulse response of the arterial system is the time domain equivalent of its input impedance in the frequency domain, they emphasize different aspects of the system. Figure 2 shows the aortic input impedance (Zi) and its corresponding impulse response of the same normal rat shown in Fig. 1. The impedance modulus fell steeply from a high value at zero frequency (i.e., peripheral resistance) to extremely low values at high frequencies that fluctuated around the aortic characteristic impedance (Zc) (Fig. 2A). The impedance phase indicates the delay between the corresponding pressure and flow components (Fig. 2B). By contrast, Fig. 2D shows the 2 discrete reflection peaks in the impulse response curve, which was calculated through the inverse transformation of Zi filtered by a Dolph-Chebychev weighting function (Fig. 2C). Half of the time difference between the long and short arrows approximates the arterial τw in the lower body circulation. In this case, the arterial τw was 27.9 ms.

Bottom Line:
The accurate measurement of arterial wave properties in terms of arterial wave transit time (τw) and wave reflection factor (Rf) requires simultaneous records of aortic pressure and flow signals.However, in clinical practice, it will be helpful to describe the pulsatile ventricular afterload using less-invasive parameters if possible.Arterial wave reflections were derived using the impulse response function of the filtered aortic input impedance spectra.

Affiliation:
Department of Physiology, College of Medicine, National Taiwan University, Taipei, 100, Taiwan.

ABSTRACTThe accurate measurement of arterial wave properties in terms of arterial wave transit time (τw) and wave reflection factor (Rf) requires simultaneous records of aortic pressure and flow signals. However, in clinical practice, it will be helpful to describe the pulsatile ventricular afterload using less-invasive parameters if possible. We investigated the possibility of systolic aortic pressure-time area (PTAs), calculated from the measured aortic pressure alone, acting as systolic workload imposed on the rat diabetic heart. Arterial wave reflections were derived using the impulse response function of the filtered aortic input impedance spectra. The cardiovascular condition in the rats with either type 1 or type 2 diabetes was characterized by (1) an elevation in PTAs; and (2) an increase in Rf and decrease in τw. We found that an inverse linear correlation between PTAs and arterial τw reached significance (τw = 38.5462 - 0.0022 × PTAs; r = 0.7708, P